This invention relates to a process for the production of a composite, molded article obtained from a cement.
Molded, plastic concrete bodies obtained from cement-containing W/O (water in oil) emulsions are light in weight and high in toughness and, thus, are now increasingly used as construction materials. Such plastic concrete bodies have been generally produced by a method including the steps of forming a W/O emulsion by mixing a vinyl monomer, water, an emulsifier and a polymerization initiator, mixing a cement with the W/O emulsion to form a mixture, molding the mixture, hardening the molded product by both polymerization of the monomer and the hardening of the cement.
As an emulsifier for forming the above W/O emulsion, Japanese Published Examined Patent Application (Tokkyo Kokoku) No. 64-341 proposes the use of an esterification product obtained by reaction of a polyalkylene glycol having an average molecular weight of 2,000-3,000 with a dibasic acid anhydride. With such an emulsifier, however, the emulsion has so low a viscosity that it is impossible to form a plate by extrusion thereof. Further, since a relatively large amount of a vinyl monomer is needed to form the emulsion, the final molded product fails to show satisfactory flame resistance.
To cope with these problems, Japanese Tokkyo Kokoku No. 1-30778 suggests the use of an ester-containing nonionic surfactant having an HLB value of 3-5, such as sorbitan monooleate as an emulsifier. While the use of the surfactant permits the molding of the emulsion by extrusion and the reduction of the amount of the vinyl monomer, there is caused a problem because the ester is susceptible to hydrolysis so that the emulsion is not stable. Additionally, since the emulsifier is not completely soluble in the monomer, undissolved matters tend to accumulate or deposit on the bottom of a mixer, a storage tank or pipes connected thereto. This necessitates periodical cleaning of the apparatus.